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media: field-order.rst: clarify FIELD_ANY and FIELD_NONE 

Rephrased the FIELD_ANY description: rather than explicitly list
field values, just say 'when any field format is acceptable'. The
list of FIELD values was outdated, so it was a bit confusing.

The FIELD_NONE description said that 'The driver may also indicate
this order when it cannot distinguish between V4L2_FIELD_TOP and
V4L2_FIELD_BOTTOM'. This is false, NONE really means a full frame
and userspace depends on that. So drop this line completely. There
are no drivers that do this anyway.

FIELD_TOP/BOTTOM/ALTERNATE indicate that the number of lines in the
buffer are that of a field, not frame, so returning NONE here would
cause huge problems.

Finally attempt to clarify 'progressive' and 'interlaced' a little
bit.

Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
hifive-unleashed-5.2
Hans Verkuil 2019-04-23 10:05:09 -04:00 committed by Mauro Carvalho Chehab
parent 16204b8a1c
commit 823a633eeb
1 changed files with 7 additions and 9 deletions
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16
Documentation/media/uapi/v4l/field-order.rst
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@ -75,12 +75,11 @@ enum v4l2_field
* - ``V4L2_FIELD_ANY``
- 0
- Applications request this field order when any one of the
``V4L2_FIELD_NONE``, ``V4L2_FIELD_TOP``, ``V4L2_FIELD_BOTTOM``, or
``V4L2_FIELD_INTERLACED`` formats is acceptable. Drivers choose
depending on hardware capabilities or e. g. the requested image
size, and return the actual field order. Drivers must never return
``V4L2_FIELD_ANY``. If multiple field orders are possible the
- Applications request this field order when any field format
is acceptable. Drivers choose depending on hardware capabilities or
e.g. the requested image size, and return the actual field order.
Drivers must never return ``V4L2_FIELD_ANY``.
If multiple field orders are possible the
driver must choose one of the possible field orders during
:ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` or
:ref:`VIDIOC_TRY_FMT <VIDIOC_G_FMT>`. struct
@ -88,9 +87,8 @@ enum v4l2_field
``V4L2_FIELD_ANY``.
* - ``V4L2_FIELD_NONE``
- 1
- Images are in progressive format, not interlaced. The driver may
also indicate this order when it cannot distinguish between
``V4L2_FIELD_TOP`` and ``V4L2_FIELD_BOTTOM``.
- Images are in progressive (frame-based) format, not interlaced
(field-based).
* - ``V4L2_FIELD_TOP``
- 2
- Images consist of the top (aka odd) field only.